Re: [Discuss-gnuradio] On Off Keying
Johnathan Corgan wrote: On Mon, Sep 29, 2008 at 2:28 PM, Brian Padalino <[EMAIL PROTECTED]> wrote: Don't some of the daughterboards also have some AGC built in? I can see if the interpolation rate is not high enough, the signal power will not go down enough (especially after the RRC filtering) to really look like much of a difference if any due to the AGC circuitry and other transients that may occur on signals quickly coming on then off. None of the daughterboards have AGC as far as I'm aware (Matt, correct me if I'm wrong on this.) It is not automatic, but there is gain control under software control. Matt ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
RE: [Discuss-gnuradio] On Off Keying
U. I thought the ADC's or an external gain element was on the USRP1. ARRL SDR Working Group Chair Member: ARRL, AMSAT, AMSAT-DL, TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. "Trample the slow Hurdle the dead" From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Firas Abbas Sent: Tuesday, September 30, 2008 3:22 PM To: Brian Padalino; Johnathan Corgan Cc: sri ram; discuss-gnuradio@gnu.org Subject: Re: [Discuss-gnuradio] On Off Keying Hi, > Johnathan Corgan <[EMAIL PROTECTED]> wrote: > > None of the daughterboards have AGC as far as I'm aware (Matt, > correct me if I'm wrong on this.) I'm not very sure, but I think TVRX daughter board has an AGC. Regards, Firas ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] On Off Keying
Hi, > Johnathan Corgan <[EMAIL PROTECTED]> wrote: > > None of the daughterboards have AGC as far as I'm aware (Matt, > correct me if I'm wrong on this.) I'm not very sure, but I think TVRX daughter board has an AGC. Regards, Firas ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] On Off Keying
Thanks for all the discussions. It has definitely given me clarity into what is happening. . I understand that the DC component of the transmitted signal, along with the frequency offset causes a strong tone at the receiver. I have linked two plots of the real part of the received baseband samples with and without RRC pulse shaping. http://www.ece.gatech.edu/~sriram/rrc.gif http://www.ece.gatech.edu/~sriram/norrc.gif It is clear that there is a strong tone corresponding to the frequency offset and the data modulation can be seen although not clearly. Also, using the RRC pulse shaping seems to be better when I observe the real part of the received sample (although the power plots are similar with and without RRC). I am just wondering how I could demodulate this and how practical OOK receivers operate. Should this tone be filtered out using a high pass filter (difference of consecutive samples?) ? Since the data sample variation is faster than the frequency offset ( about 100 samples for one cycle of the offset frequency), it looks likely that a filter which passes the high frequency (Data) variations and filters out the low frequency (frequency offset) must be helpful? Am I correct in thinking this way? Feeding this to the costas loop does not help much. The costas loop (with default parameters that work for dBpsk) is unable to demodulate the bits correctly. I am wondering if tweaking its parameters to values different from the default ones might help. I currently use a -i 256 and -d 128, since my laptops don't keep up for lower values. I will experiment to see what happens if they are increased. Thanks, Sri On 9/30/08, Johnathan Corgan <[EMAIL PROTECTED]> wrote: > > On Mon, Sep 29, 2008 at 2:28 PM, Brian Padalino <[EMAIL PROTECTED]> > wrote: > > > Don't some of the daughterboards also have some AGC built in? I can > > see if the interpolation rate is not high enough, the signal power > > will not go down enough (especially after the RRC filtering) to really > > look like much of a difference if any due to the AGC circuitry and > > other transients that may occur on signals quickly coming on then off. > > > None of the daughterboards have AGC as far as I'm aware (Matt, > correct me if I'm wrong on this.) > > It's not that the filtering is preventing the envelope from going to > zero (though it might be; RRC's are intentionally designed to > introduce ISI in a very specific way). It's just that with the > waveform he's sending, there is a strong carrier component at passband > that shows up as a constant beat frequency in the receiver due to > frequency offset. > > > > Please correct me if I am wrong, but I think using a very large > > interpolation rate might help clarify the situation. > > > It would improve things. If the baseband "square wave" had it's > fundamental frequency near the RRC filter limit, or near the Nyquist > limit of the baseband sampling rate if the RRC wasn't in use, there > would be few to no harmonics that make it through the filtering and/or > interpolation. The transmitted waveform would be a carrier and two > sidebands, a classic AM waveform. I think that's what he is seeing. > > > -- > Johnathan Corgan > Corgan Enterprises LLC > http://corganenterprises.com/ > ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] On Off Keying
On Mon, Sep 29, 2008 at 2:28 PM, Brian Padalino <[EMAIL PROTECTED]> wrote: > Don't some of the daughterboards also have some AGC built in? I can > see if the interpolation rate is not high enough, the signal power > will not go down enough (especially after the RRC filtering) to really > look like much of a difference if any due to the AGC circuitry and > other transients that may occur on signals quickly coming on then off. None of the daughterboards have AGC as far as I'm aware (Matt, correct me if I'm wrong on this.) It's not that the filtering is preventing the envelope from going to zero (though it might be; RRC's are intentionally designed to introduce ISI in a very specific way). It's just that with the waveform he's sending, there is a strong carrier component at passband that shows up as a constant beat frequency in the receiver due to frequency offset. > Please correct me if I am wrong, but I think using a very large > interpolation rate might help clarify the situation. It would improve things. If the baseband "square wave" had it's fundamental frequency near the RRC filter limit, or near the Nyquist limit of the baseband sampling rate if the RRC wasn't in use, there would be few to no harmonics that make it through the filtering and/or interpolation. The transmitted waveform would be a carrier and two sidebands, a classic AM waveform. I think that's what he is seeing. -- Johnathan Corgan Corgan Enterprises LLC http://corganenterprises.com/ ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] On Off Keying
On Mon, Sep 29, 2008 at 4:40 PM, Johnathan Corgan <[EMAIL PROTECTED]> wrote: > On Mon, Sep 29, 2008 at 11:52 AM, sri ram <[EMAIL PROTECTED]> wrote: > >> 3. However, for a tx. stream of 1's and 0's mixed, I still see the received >> amplitude (real part) showing the beat frequency continuously and not going >> to 0 for the 0 bits. > > When you send alternating 1's and 0's, you are creating a baseband > square wave of constant power. The DC offset is half your baseband > transmit amplitude, and that energy at DC is upconverted to your > carrier frequency. On receive, since you have a frequency offset, you > will see a continuous beat frequency resulting from this constant > carrier. Superimposed on this will be the harmonics of your square > wave up to the Nyquist limit of your baseband sampling rate, or up to > the cutoff frequency of the RRC filter if it is in use. Don't some of the daughterboards also have some AGC built in? I can see if the interpolation rate is not high enough, the signal power will not go down enough (especially after the RRC filtering) to really look like much of a difference if any due to the AGC circuitry and other transients that may occur on signals quickly coming on then off. Please correct me if I am wrong, but I think using a very large interpolation rate might help clarify the situation. Brian ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] On Off Keying
On Mon, Sep 29, 2008 at 11:52 AM, sri ram <[EMAIL PROTECTED]> wrote: > 3. However, for a tx. stream of 1's and 0's mixed, I still see the received > amplitude (real part) showing the beat frequency continuously and not going > to 0 for the 0 bits. When you send alternating 1's and 0's, you are creating a baseband square wave of constant power. The DC offset is half your baseband transmit amplitude, and that energy at DC is upconverted to your carrier frequency. On receive, since you have a frequency offset, you will see a continuous beat frequency resulting from this constant carrier. Superimposed on this will be the harmonics of your square wave up to the Nyquist limit of your baseband sampling rate, or up to the cutoff frequency of the RRC filter if it is in use. You could of course change your baseband to be bipolar (-1, 1), but then again, that's just BPSK. -- Johnathan Corgan Corgan Enterprises LLC http://corganenterprises.com/ ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
[Discuss-gnuradio] On Off Keying
Hi, I am trying to send a stream of bits using On Off keying and am having some issues. At this stage, I just want to check if 1's and 0's are getting received with a high and low amplitude respectively. I have modified dbpsk.py setting the constellation to 0+0i and 1+0i in psk.py and invoke the tx/rx as in benchmark_tx,benchmark_rx .. My flowgraph is Bytes2symbols ->RRCFilter->USRP USRP->filesink I have a Bytes2symbols file which just writes the complex symbols for a given set of bytes as in gr_chunks2symbols_bc.cc. I have also checked that the complex symbols entering the USRP at the transmitter are as expected. However, at the receiver (USRP baseband samples without any processing) when I measure the power, I do not see the power going low for the 0 bits. Specifically, when I send a 101010... bit stream of 128 samples (just these bits without any headers/trailers). The transmitted baseband complex symbols are as expected with the real part going between 1 and 0 alternatively. *At the receiver, the received power stays almost the same high value throughout the packet duration, whereas I would have expected it to alternatively go high and low*. Adding or removing the RRC filter doesn't affect the observation. The following observations are true for the power and the real part of the baseband samples. 1. For a tx. stream of all 1's, i can see the beat frequency or the frequency offset for the duration of the packet (as expected). 2. For a tx. stream of all 0's , i see a low received value. (almost close to the noise levels) as expected. 3. However, for a tx. stream of 1's and 0's mixed, I still see the received amplitude (real part) showing the beat frequency continuously and not going to 0 for the 0 bits. I am using the latest stable version i.e gnuradio-3.1.3 on Ubuntu laptops. Could this be Inter Symbol Interference or a setting which makes the (carrier) power coming out of the USRP constant for the packet duration irrespective of the tx.data? Any help is greatly appreciated. Thanks, Sri. ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
